A standard drill chuck as described in U.S. Pat. No. 5,765,839 has a chuck body rotatable about a chuck axis and provided centered on the axis with an annular array of teeth each having a steep flank and a shallow flank. Jaws angularly spaced on the body about the axis are radially displaceable relative to the body between inner and outer positions. A tightening ring is axially fixed but rotatable about the axis on the body in a tightening direction and in an opposite loosening direction. A pair of screwthread formations between the tightening ring and the jaws move the jaws radially together on rotation of the tightening ring in the tightening direction and radially apart on rotation of the tightening ring in the loosening direction. A locking member engageable with the teeth and angularly fixed on the tightening ring is radially displaceable between a locking position engaging the teeth and preventing rotation of the body relative to the tightening ring in the loosening direction and a freeing position permitting free rotation of the body relative to the tightening ring in both directions. A setting ring axially fixed but angularly displaceable on the tightening ring is formed with a pair of angularly spaced and radially open seats. A pair of angularly spaced abutments between the setting ring and the tightening ring limit angular movement of the sleeve on the ring to movement between a pair of end positions of the sleeve on the ring. A cam on the setting ring is engageable with the locking member for displacing the locking member into the locking position when the setting ring is in one of its end positions and for displacing the locking member into the freeing position when the setting ring is in the other of its end positions. A latch member angularly fixed on the tightening ring is engageable in the seats of the setting ring for releasably retaining the setting ring in its end positions. A common spring extending angularly along and fixed angularly in the tightening ring urges the latch member into the seats and the locking member into the freeing position.
Such a chuck is normally mounted on a spindle of a power unit and is operated in so-called power-open or power-close mode by gripping and manually arresting the tightening ring while operating the power unit to rotate the spindle in forward or reverse to shift the jaws appropriately. This procedure has the disadvantage that the considerable torque of the spindle, which is rotating at a good speed, is applied to the jaws at the ends of their travel, often jamming them in place or at best subjecting the various parts to considerable stress.